1. Field of the Invention
Rotatable printing cylinders have long been in use in the printing field. These rotatable printing cylinders are adapted to have printing mats attached to their outer cylindrical surfaces. The mats are and have been made of many different materials and the means of attaching the mats to the cylinders have taken many forms. Many mats have had their ends bent to form flanges which when disposed radially were adapted to be removably locked or wedged in radially disposed grooves in the surface of the cylinder. It has been a difficult job to mechanically lock a mat in a proper position on a cylinder and when the mats had to be changed frequently the setting up of the mat on the cylinder became almost intolerable.
A substantial breakthrough for easing this situation occurred when printing cylinders were built with permanent magnets in the cylindrical surface to receive and hold printing mats without auxiliary mechanical attaching means. Such magnetic mat attachment worked ideally when the base cylinder was of relatively large diameter. However, with smaller diameter printing cylinders the magnetically attracted mats had a tendency to pull away from the cylinder at their leading and trailing ends.
It is with this as a background that the present inventor developed a sure means for magnetically holding the full length of a printing mat to a cylinder surface regardless of the diameter of that cylinder.
2. Description of the Prior Art
A Preliminary patent search disclosed the following art which was deemed of pertinence to a consideration of patentability.
McWhorter U.S. Pat. No. 2,668,497
Kessler U.S. Pat. No. 2,978,980
Stromme U.S. Pat. No. 2,982,207
Willard U.S. Pat. No. 3,006,277
McKay U.S. Pat. No. 3,180,259
Wessels U.S. Pat. No. 3,587,464
Jenkins U.S. Pat. No. 3,885,497
Jenkins U.S. Pat. No. 3,885,498
Saunders et al U.S. Pat. No. 3,934,509
The patents to McWhorter, kessler, Wessels and Saunders et al all show various mechanical means for attaching a printing plate to a cylinder and no one of them uses any magnetic means in such attachment. These prior patents were believed to be pertinent in that the flexible printing plates shown therein have variously formed ends to facilitate the attachment of the plates to the cylinders. For example, the McWhorter patent shows and described undercut grooves 31 and 32 extending transversely near the lead- and trailing ends of a flexible plate. However, such undercut grooves do not aid in the magnetic holding of a flexible printing plate to a cylinder.
The Willard patent shows an inflatable means for locking a printing mat to a cylinder, but again there is no magnetic gripping means involved in this device.
The two Jenkins patents describe cylinder constructions with magnets incorporated therein. These Jenkins cylinders are provided with radial grooves to receive a slightly bent end of the flexible printing plates, P. The engagement of the bent end of the leading edge of the printing plate with the radial cylinder groove 21 has the stated purpose of preventing the plate from creeping around the cylinder. This is quite different from applicant's construction which is concerned only with a smooth surface, non-grooved magnetic cylinder.
The McKay patent shows another form of magnetic cylinder construction. However, there does not appear to be any similarity between the attaching means of this McKay patent and applicant's device.
The Stromme patent shows a printing plate, which is corrugated throughout its length. The Stromme plate is stated to be flexible and adheres to a magnetized cylinder. However, such a fully corrugated cylinder is not too feasible for the reception of type or other printing elements on the surface thereof because of its sawtooth surface. If fillers were used to level the V-grooves to receive type on a flat surface, a considerable amount of the plate's flexibility would be lost and the plate would be very costly to produce. There appears to be a great difference between this Stromme device and applicant's device.
Nowhere in this mass of prior art is there any teaching of applicant's invention.